[reed13k]

I know from a radiation perspective water is a good shield - especially with the amounts referred to.

I would assume that the polarization of H2O atoms, it’s direct contact with ground, and the vast volume that it would allow for a very effective EMP resistance as well. Though I’m unaware of any testing on same.

[Mariner]

"would allow for a very effective EMP resistance as well"

The EMP will enter via the power cables.